1. Field of the Invention
The present invention relates to a method for sterilizing laminated packaging material for forming a packing container to preserve a liquid such as juice or milk contained therein for a long period of time. More particularly, the present invention relates to a method for sterilizing a packaging material obtained by forming an elongated hollow packaging material including a paper layer therein into a sleeve having a predetermined length.
2. Description of the Related Art
There are two conventional methods for sterilizing packing containers.
According to the first conventional method, a sheet-like continuous laminated packaging material including a paper layer is sterilized with a hydrogen peroxide (H.sub.2 O.sub.2) solution, and the hydrogen peroxide solution is dried and removed with hot air or the like. The sheet-like packaging material sterilized by this method is formed into a tube, and one end of the tube is then sealed. A predetermined liquid is poured in the tube, and a portion below the liquid surface is sealed. The resultant packaging material containing the liquid therein is cut at predetermined positions, thereby obtaining individual containers each containing the liquid.
According to the second conventional method, a sterilized laminated continuous packaging material is cut into blanks each having a predetermined length. A container having an opening and a predetermined shape is formed from each blank. A hydrogen peroxide solution is sprayed inside the container to sterilize its inner surface. The container is heated and dried with hot air to remove the hydrogen peroxide solution. A liquid is then poured in the container, and the container is sealed, thereby finishing a container filled with a liquid.
According to the first conventional method, it is easy to sterilize the packaging material. In addition, sterilization, drying, filling of a liquid, sealing below the liquid surface, and cutting are performed in the order to seal the liquid in the container. Even if a packaging material is a laminated material including a paper layer, the liquid contained in the container is not adversely affected by cut end faces and paper dust produced by cutting. In addition, there is no head space for air left inside the container and collected at the top portion of the container. Therefore, the first conventional method is advantageous in long-term preservation. Furthermore, the first conventional method is advantageous in that no hydrogen peroxide is left at a folded portion since the sealed packaging material is folded at predetermined positions to form individual containers.
The shape of the packing containers manufactured by the first conventional method is limited to a brick-like shape since the liquid is poured in the tube-like packaging material and the packaging material is sealed and formed into a predetermined shape. Since the individual containers are obtained after the liquid is sealed in the tube-like container material, the packaging material must be flexible. Therefore, it is difficult to form the packing container by a rigid material. For this reason, when a large amount of liquid is filled in a large packaging material, each individual container is deformed by the weight of the liquid. Therefore, the first conventional method is not suitable for manufacturing large containers.
Since each individual container is formed by sealing the packaging material below the surface of liquid contained in the packaging material, a head space which is disadvantageous in food preservation can be eliminated. However, there is a fear for spilling of the contained liquid at the time of opening the container. When the container is used for a liquid containing a solid substance such as juice or soup, the solid substance may be trapped at the sealed portion, thus causing incomplete sealing.
According to the second conventional method, a container having a predetermined length is sterilized and then a liquid is filled therein. Even if a liquid containing a solid substance is filled therein, there is no fear of trapping of the solid substance at the sealing portion. In addition, a head space is assured, and the liquid is not split when the container is opened.
According to the second conventional method, however, since the elongated continuous packaging material is cut into blanks each having a predetermined length and a container is formed from each blank, paper dust is produced during cutting of the packaging material into the blanks. In addition, nonsterilized end faces are formed. During formation of an empty container by folding the packaging material, the paper dust may be trapped at the folded portion. In addition, the nonsterilized end face is exposed inside the container at the folded portion. For this reason, it is difficult to maintain the packing container in a perfect aseptic state. The packing container sterilized by the second conventional method is not suitable for preserving the liquid for a long period of time.
In a columnar container formed from a rectangular blank and having a gable-like upper portion and a flat bottom portion, cut end faces are not exposed inside the container. For this purpose, one edge of the blank is bent outward, and the folded portion is sealed on the inner surface of the other edge. In this container, a step is formed on the inner surface, and the hydrogen peroxide solution serving as a sterilizing agent tends to be left at the step portion.